Electrochemical etching of semiconductors under anodic conditions can lead to the growth of pores under conditions both of darkness and of illumination. In previous work our group has developed a new technique which uses contrast enhanced microscopy to image full electrode surfaces simultaneously with electrochemical control of the potential at the electrode-electrolyte interface. In this paper, we present results obtained using the technique to monitor in situ the InP-electrolyte interface during linear potential sweeps (LPSs) and also to investigate selective photo- electrochemical etching.