The classic technique for measuring soil water content using heat dissipation properties was employed to develop a new single probe heat pulse sensor (SPHP). The novel sensor is comprised of only one element, a npn junction bipolar transistor, which works as both heating and temperature sensing elements. The variations of V-BE(T) as a function of the temperature are used to measure the temperature of the sensor and, since the behaviour of V-BE(T) is one of the most well studied expressions that describe the bipolar transistor, the sensor's temperature can be easily measured, with high accuracy. A technique which increases simultaneously the collector-base voltage V-CB and the collector current I-C of the transistor allows for the application of the heat pulse with low level currents, in the order of 6 mA. The sensor developed in this work presented a Delta T-max range of 9.1 degrees C between wet and dry soil conditions (theta(nu) between 5% and 35%), while the current available heat pulse probe sensors present a typical Delta T-max range of only 1.5 degrees C, showing the potential benefits of using a single bipolar junction transistor as a high sensitivity soil water content measurement sensor. (C) 2013 Elsevier B.V. All rights reserved.96139147