A new model for the analysis of resist heating is proposed and applied to the direct electron beam writing method using a variably‐shaped electron beam system and a single‐layer resist. From calculations based on the present model and experiment, it was found that the resist heating effect leads to resist ablation, difference in resist sensitivity between single exposure and multiple exposures, and depth dependence and beam size dependence of resist sensitivity. It also explains the degradation of shaped beam stitching accuracy as well as pattern size error. The resist heating effect is more serious for direct writing than the estimation obtained from a conventional model. In order to realize submicron patterns below 0.5 μm with considerable high throughput, the use of a highly sensitive resist is essential for overcoming the resist heating effect.