A novel simple bottom-electrode metal-semiconductor-metal photodetector (BMSM-PD) with an i-a-Si:H barrier layer and a phosphorus-doped n-a-Si:H light absorbing layer was used to improve the responsivity of MSM-PD. Ar a bias of 10V and an He-Ne laser incident power of 10 mu W, the obtained n-a-Si:H BMSM-PD had a high responsivity of 10A/W, a low dark current density of 2.35pA/mu m(2), and a spectral response peaked at 605 nm.