Heterojunction cells of p-MgPc/n-Si have been fabricated by thermal evaporation of MgPc thin films onto Si < 100 > single crystal wafers. The devices exhibit strong photovoltaic characteristics with an open-circuit voltage of 0.35 V, a short-circuit current of 3.57 mA and a power conversion efficiency of 1.05%. These parameters have been estimated at room temperature and under a monochromatic illumination of 633 nm with an input power density of 50 mW/cm(2). The activation energy of the charge carriers of 0.32 eV and the cell series resistance of 2 k Omega have been evaluated from the measurements of the dark I-V characteristics. A free-carrier concentration of 2.2 x 10(16) cm(-3) and a barrier width of 75 nm have been estimated from C-V measurements. The temperature dependence of photocurrent, at constant illumination, has been also investigated.