Finite-difference calculations were used to characterize a periodic alternation of heating and nonheating of finite and semi-infinite regions. Heating with a fixed heat flux density and heating with a fixed temperature at the surface or surfaces were both examined. Theoretically based correlating equations were developed to generalize the computed values. Periodic on-off heating with a fixed heat flux density is shown to be particularly advantageous when deep and rapid penetration of energy is to be accomplished while constraining the maximum temperature at the surface.