The photoelectrochemical behavior of polycrystalline diamond films, grown on tungsten substrates by chemical vapor deposition (CVD), has been studied in 0.5M solution. Different types of films have been investigated, with or without intentional doping with boron. Experimental results point to a p‐type behavior of boron‐doped samples, while the presence of an inversion of the photocurrent sign reveals an insulating behavior of undoped samples. Photocurrent spectra display different threshold energies, which have been related with possible defect levels inside both types of diamond films.