A non-genetic photostimulation platform based on semiconductor-enabled biomodulation interfaces is introduced for high spatiotemporal cardiac stimulation. The platform uses monolithic silicon-based photoelectrochemical devices to achieve precise and tunable photostimulation in cardiac systems. The study demonstrates the optoelectronic capabilities of these devices through various experiments, including optical overdrive pacing of cultured cardiomyocytes (CMs), isolated rat hearts in a Langendorff apparatus, in vivo rat hearts in an ischaemia model, and an in vivo mouse heart model with transthoracic optical pacing. The system is adaptable for minimally invasive clinical procedures using a custom endoscopic delivery device, enabling closed-thoracic operations and endoscopic optical stimulation. The results indicate the clinical potential of the leadless, lightweight, and multisite photostimulation platform as a pacemaker in cardiac resynchronization therapy (CRT), where lead-placement complications are common. Leadless flexible bioelectronics that modulate bioelectrical signaling in a manner similar to the body's own regulatory mechanisms can offer new treatment paths for neurodegenerative and cardiac diseases. Optically mediated genetic systems offer high spatiotemporal resolution and tunability, with random-access capabilities for cellular and tissue stimulation. For clinical translation, recent non-genetic photodiode-based optoelectronic devices, which convert light into electrical currents, efficiently modulate cells and tissues at optical-power levels comparable with those used in optogenetics. Micropatterned pixelated optoelectrodes that enable localized stimulation with high resolution demonstrate great potential for retinal prosthesis. The study systematically assesses the spatiotemporal profiles of photoelectrochemical current generation and dynamics in four variations of monolithic Si-based photoelectrochemical devices to delineate multisite photostimulation capability in biological systems. Their capacity for multiscale configurations suggests new opportunities in biological interfaces. The study demonstrates multiscale spatiotemporal cardiac modulation in in vitro-cultured rat CMs and ex vivo and in vivo rat heart models. A tissue-penetrating photostimulation experiment in a mouse heart in vivo illustrates non-invasive stimulation. Reliable multisite cardiac control with millisecond-duration light pulses is demonstrated in a live pig heart experiment under clinical open-thoracic conditions. Closed-thoracic pig heart stimulation using a custom endoscopic operation system is also demonstrated, highlighting translational potential. Beyond biointerface research, the capacity for spatial manipulation of photoelectrochemical current polarity on a monolithic semiconductor surface has wide-ranging implications in energy science and catalysis. The study introduces spatiotemporal photoelectrochemical device profiling as a new approach to assess spatiotemporal capability in semiconductor–saline systems. The study fabricates four Si-based photodiode devices with distinct configurations and evaluates their performance in terms of photocurrent magnitude, precision, accuracy, and resolution. The results show that Por-Si offersA non-genetic photostimulation platform based on semiconductor-enabled biomodulation interfaces is introduced for high spatiotemporal cardiac stimulation. The platform uses monolithic silicon-based photoelectrochemical devices to achieve precise and tunable photostimulation in cardiac systems. The study demonstrates the optoelectronic capabilities of these devices through various experiments, including optical overdrive pacing of cultured cardiomyocytes (CMs), isolated rat hearts in a Langendorff apparatus, in vivo rat hearts in an ischaemia model, and an in vivo mouse heart model with transthoracic optical pacing. The system is adaptable for minimally invasive clinical procedures using a custom endoscopic delivery device, enabling closed-thoracic operations and endoscopic optical stimulation. The results indicate the clinical potential of the leadless, lightweight, and multisite photostimulation platform as a pacemaker in cardiac resynchronization therapy (CRT), where lead-placement complications are common. Leadless flexible bioelectronics that modulate bioelectrical signaling in a manner similar to the body's own regulatory mechanisms can offer new treatment paths for neurodegenerative and cardiac diseases. Optically mediated genetic systems offer high spatiotemporal resolution and tunability, with random-access capabilities for cellular and tissue stimulation. For clinical translation, recent non-genetic photodiode-based optoelectronic devices, which convert light into electrical currents, efficiently modulate cells and tissues at optical-power levels comparable with those used in optogenetics. Micropatterned pixelated optoelectrodes that enable localized stimulation with high resolution demonstrate great potential for retinal prosthesis. The study systematically assesses the spatiotemporal profiles of photoelectrochemical current generation and dynamics in four variations of monolithic Si-based photoelectrochemical devices to delineate multisite photostimulation capability in biological systems. Their capacity for multiscale configurations suggests new opportunities in biological interfaces. The study demonstrates multiscale spatiotemporal cardiac modulation in in vitro-cultured rat CMs and ex vivo and in vivo rat heart models. A tissue-penetrating photostimulation experiment in a mouse heart in vivo illustrates non-invasive stimulation. Reliable multisite cardiac control with millisecond-duration light pulses is demonstrated in a live pig heart experiment under clinical open-thoracic conditions. Closed-thoracic pig heart stimulation using a custom endoscopic operation system is also demonstrated, highlighting translational potential. Beyond biointerface research, the capacity for spatial manipulation of photoelectrochemical current polarity on a monolithic semiconductor surface has wide-ranging implications in energy science and catalysis. The study introduces spatiotemporal photoelectrochemical device profiling as a new approach to assess spatiotemporal capability in semiconductor–saline systems. The study fabricates four Si-based photodiode devices with distinct configurations and evaluates their performance in terms of photocurrent magnitude, precision, accuracy, and resolution. The results show that Por-Si offers