The sensitivity of a thermal flow sensor is investigated in this study. A simple numerical model for analyzing heat transfer phenomena in the thermal flow sensor is presented. In order to validate the proposed model, experimental investigations are performed. Based on the results from the validated model, a correlation that predicts the sensitivity of the thermal flow sensor is presented. From the correlation, the manner in which the heat loss, the positions of the temperature sensors, the input power, and the heater length affect the sensitivity of the thermal flow sensor is investigated. (C) 2008 Elsevier Ltd. All rights reserved.