Photoelectrochemical (PEC) studies of p-InP in various nitric acid solutions demonstrated that the semiconductor undergoes etching with favorable etch rates in the negative potential region. The etch rate increases with decreasing potentials to -1.0 V and exhibits a small decrease with still lower potentials. Etch rates are proportional to light intensity. The values of etch rate for p-InP biased at -1.0 V vary from 0.07 to 1.24 mu m/min for HNO3 solutions with concentrations ranging from 1.0 to 5.0 M. With acid concentrations greater than 5 M, the etch rates were inconsistent. Little or no PEC etching was observed with nitric acid concentrations greater than 7.5 M. Voltammetry shows that photoreduction of protons and possibly nitric acid takes precedence over the photoreduction of InP to In in higher HNO3 concentrations.