Laser transformation hardening is a versatile technique for enhancing surface hardness, but it has been mostly used for hardening of thick plates in order to secure enough self-quenching effect. Recently, there have been increasing needs for heat treating steel sheets, but the understanding of heat treatability for metal sheets is limited. In this study, we have investigated the effect of specimen thickness on hardening performance in the laser heat treatment of carbon steel using the process map approach recently proposed by Ki and So (2012) [1]. Using a one-dimensional heat conduction model, we have studied how the process map evolves as the specimen thickness decreases. For validation purposes, we have systematically conducted laser heat treatment on AISI 1020 steel specimens using a 3 kW diode laser and constructed surface hardness maps. The experimental results are in good agreement with the theoretical predictions. (C) 2013 Elsevier Ltd. All rights reserved.