A simple analytical model that predicts the temperature rise of a small heater on an unheated substrate is presented. The model approximates uniform temperature over both the healer and the substrate, although they have spatial distributions in actual case. A rigorous numerical calculation has been performed to verify the model results. A regime map is constructed based on the analytical model. Each regime in the map is named in order to show the time dependency and the governing heal transfer mode of the healer temperature rise.