High quality semiconducting boron-doped polycrystalline diamond thin films were prepared on Si substrates via microwave plasma chemical vapor deposition. The resistivities of the lightly doped films were on the order of 10(2) Omega cm. The photoelectrochemical behavior was studied with excimer lasers of several different wavelengths, including ArF (193 nm, 6.4 eV), KrF (248 nm, 5.0 eV), and XeF (351 nm, 3.53 eV). The photocurrent observed using the ArF laser was significantly greater than those observed with the KrF and XeF lasers. We propose that, for the ArF laser, the suprabandgap illumination was able to excite electrons into the conduction band, while the KrF and XeF lasers were not.