The multiphoton ionization of a low‐pressure (3×10−5Torr) fill of trimethylamine using an electron‐beam pumped KrF laser has been studied. A microwave resonator probe was used to measure the resultant free‐electron density. The scaling of electron density with the square of the incident laser intensity was verified in the low flux limit. The electron production decreased significantly from theI2scaling at laser fluxes exceeding 4 MW/cm2. These results are consistent with a simple two‐photon model describing the interaction in the low flux limit and a saturation of the electron production in the high‐flux limit. ©1996 American Institute of Physics.