A systematic study of semiconductor-insulator-semiconductor (SIS) solar cells has been undertaken on n-type Si and GaAs using spray-deposited indium-tin oxide (ITO) for the window layer of the heterostructure. The optical and electrical characteristics of the ITO layer as well as the thickness of the I-layer have been optimized to yield the following photovoltaic parameters on 1 Ω-cm n-Si: Voc=0.52 V, Jsc=31.5 mA/cm2 (adjusted for Ag grid area), FF=0.70 and effective area η=11.5%. The dark I-V and C-V characteristics have also been evaluated to identify the mechanisms of barrier formation and current flow.