The structure and resistivity of vanadium dioxide films close to the metal‐semiconductor transition have been studied as a function of stoichiometry. Unit‐cell volume is shown to go through a minimum and the transition temperature and resistivity ratio through a maximum at the apparent stoichiometric oxygen level. The observed resistivities can be accounted for by an increased electron concentration due to vanadium interstitials in the low‐oxygen films and by a second phase in the high‐oxygen films. The variation of resistivity and transition temperature with electron concentration provides experimental support for the previous suggestion that the driving force of the transition is mainly an antiferroelectric distortion.