Energy conversion efficiencies as high as 5.96% are reported on polycrystalline transparent magnesium Zn3P2diodes, 0.7 cm2in area, tested under simulated AM1 illumination. The transparent Mg films with low sheet resistivities are obtained by dc sputtering. The effective minority‐carrier diffusion length in Zn3P2is estimated from spectral response measurements and correlates well with the measured short‐circuit current. Loss analysis of the present cells shows a practical upper limit of 9% in conversion efficiency.