Three‐dimensional electron optical simulations were used to model scanning tunneling microscope (STM) lithography in resists under field emission conditions. This work focuses on the effect of resists, as dielectric layers, between the tip and conducting substrate on the operation of the STM. Simulations were performed for resist thicknesses of 1–50 nm and tip‐resist separations of 1–20 nm. For a fixed 10 nm tip‐resist separation, the axial electric field at the tip decreases by a factor of 2.3 over the resist thickness range. The results show that the tip‐resist separation must decrease with increasing resist thickness, to achieve the operating conditions and the energy of electrons entering the resist can be significantly less than the applied tip‐substrate bias. ©1996 American Institute of Physics.