Black phosphorus field-effect transistors (FETs) based on few-layer black phosphorus crystals have been successfully fabricated, demonstrating promising performance for future nano-electronic applications. The devices exhibit high drain current modulation (up to $10^5$) and field-effect mobility (up to $1000\ \text{cm}^2/\text{Vs}$) at room temperature. The mobility is thickness-dependent, with the highest value achieved at $ \sim 10 $ nm. Black phosphorus, a layered material with a direct band gap of $ \sim 2 $ eV, shows potential for optoelectronics and nano-electronics due to its thickness-dependent band gap and unique electronic properties. The devices exhibit ambipolar behavior, with carrier sign inversion observed in the "on" states, indicating Fermi level shifting between the valence and conduction bands. The performance of the FETs is comparable to those based on other layered materials, with high drain current modulation and mobility values. The results suggest that black phosphorus is a promising candidate for high-speed field-effect devices. The mobility is limited by charge impurity scattering at low temperatures and electron-phonon scattering at high temperatures. The study also explores the temperature dependence of carrier mobility, showing that it decreases with increasing temperature. The findings highlight the potential of black phosphorus in future nano-electronic and opto-electronic applications.Black phosphorus field-effect transistors (FETs) based on few-layer black phosphorus crystals have been successfully fabricated, demonstrating promising performance for future nano-electronic applications. The devices exhibit high drain current modulation (up to $10^5$) and field-effect mobility (up to $1000\ \text{cm}^2/\text{Vs}$) at room temperature. The mobility is thickness-dependent, with the highest value achieved at $ \sim 10 $ nm. Black phosphorus, a layered material with a direct band gap of $ \sim 2 $ eV, shows potential for optoelectronics and nano-electronics due to its thickness-dependent band gap and unique electronic properties. The devices exhibit ambipolar behavior, with carrier sign inversion observed in the "on" states, indicating Fermi level shifting between the valence and conduction bands. The performance of the FETs is comparable to those based on other layered materials, with high drain current modulation and mobility values. The results suggest that black phosphorus is a promising candidate for high-speed field-effect devices. The mobility is limited by charge impurity scattering at low temperatures and electron-phonon scattering at high temperatures. The study also explores the temperature dependence of carrier mobility, showing that it decreases with increasing temperature. The findings highlight the potential of black phosphorus in future nano-electronic and opto-electronic applications.