Black phosphorus (BP) is a layered material with a structure similar to graphene, allowing for the mechanical exfoliation of ultrathin single crystals. This study demonstrates field effect devices using few-layer BP on Si/SiO₂ and measures charge carrier mobility and drain current modulation. Room-temperature mobilities of up to 300 cm²/Vs and drain current modulation of over 10³ were observed. At low temperatures, the on-off ratio exceeds 10⁵, and the device exhibits both electron and hole conduction. Atomic force microscopy (AFM) shows significant surface roughening of BP crystals within an hour after exfoliation, likely due to oxidation and degradation. Few-layer BP was obtained by cleaving bulk BP using the scotch-tape method and deposited onto Si/SiO₂ wafers. The crystals were characterized using optical microscopy, AFM, and Raman spectroscopy. The AFM images revealed surface roughness, which increased over time due to oxidation. To minimize degradation, PMMA was quickly applied to the exfoliated flakes. Electrical contacts were defined using electron-beam lithography, and Ti/Au electrodes were fabricated. The devices were measured in both four-point and two-point configurations. The four-point configuration was used to extract mobility, while the two-point configuration measured drain current modulation. The four-point conductance versus back gate voltage showed a mobility of ~300 cm²/Vs. The I-V characteristics confirmed ohmic contacts at negative gate voltages. The drain current modulation was measured at various temperatures, showing a significant hysteresis at higher temperatures, which decreased at low temperatures. The device exhibited ambipolar transport, with higher mobility on the hole side. The hysteresis was attributed to surface degradation and charge trapping. The mobility of few-layer BP was lower than that of bulk BP, suggesting that ambient conditions affect performance. Encapsulation with materials like boron nitride may be necessary for devices with carrier mobilities comparable to bulk BP. This study highlights the potential of BP for next-generation two-dimensional electronic devices.Black phosphorus (BP) is a layered material with a structure similar to graphene, allowing for the mechanical exfoliation of ultrathin single crystals. This study demonstrates field effect devices using few-layer BP on Si/SiO₂ and measures charge carrier mobility and drain current modulation. Room-temperature mobilities of up to 300 cm²/Vs and drain current modulation of over 10³ were observed. At low temperatures, the on-off ratio exceeds 10⁵, and the device exhibits both electron and hole conduction. Atomic force microscopy (AFM) shows significant surface roughening of BP crystals within an hour after exfoliation, likely due to oxidation and degradation. Few-layer BP was obtained by cleaving bulk BP using the scotch-tape method and deposited onto Si/SiO₂ wafers. The crystals were characterized using optical microscopy, AFM, and Raman spectroscopy. The AFM images revealed surface roughness, which increased over time due to oxidation. To minimize degradation, PMMA was quickly applied to the exfoliated flakes. Electrical contacts were defined using electron-beam lithography, and Ti/Au electrodes were fabricated. The devices were measured in both four-point and two-point configurations. The four-point configuration was used to extract mobility, while the two-point configuration measured drain current modulation. The four-point conductance versus back gate voltage showed a mobility of ~300 cm²/Vs. The I-V characteristics confirmed ohmic contacts at negative gate voltages. The drain current modulation was measured at various temperatures, showing a significant hysteresis at higher temperatures, which decreased at low temperatures. The device exhibited ambipolar transport, with higher mobility on the hole side. The hysteresis was attributed to surface degradation and charge trapping. The mobility of few-layer BP was lower than that of bulk BP, suggesting that ambient conditions affect performance. Encapsulation with materials like boron nitride may be necessary for devices with carrier mobilities comparable to bulk BP. This study highlights the potential of BP for next-generation two-dimensional electronic devices.