Plasma source ion implantation (PSII) is a plasma-based ion implantation technique which requires pulsed operation. Because the power incident on the implanted objects (targets) can be large, target temperatures can be quite high. Therefore, target temperature prediction can be quite useful, both in reaching high temperatures when they are desirable, and in avoiding high temperatures when they are undesirable. In this paper, a simple, time-dependent, lumped-capacity thermal model is developed for predicting temperatures in PSII targets. Two simple analytical models are used to justify the assumptions used in developing the lumped model. Comparison of the model with measured target temperatures is used to validate the assumptions of the model. The comparison is favorable.