As one of the most environmentally important cations, mercury(II) iron has the biological toxicity which impacts wild life ecology and human health heavily. A Hg2+ biosensor based on AlGaAs/InGaAs high electron mobility transistors with high sensitivity and short response time is demonstrated experimentally. To achieve highly specific detection of Hg2+, an one-end thiol-modified ssDNA with lots of T thymine is immobilized to the Au-coated gate area of the high electron mobility transistors by a covalent modification method. The introduction of Hg2+ to the gate of the high electron mobility transistors affects surface charges, which leads to a change in the concentration of the two-dimensional electron gas in the AlGaAs/InGaAs high electron mobility transistors. Thus, the saturation current curves can be shifted with the modification of the gate areas and varied concentrations of He2+. Under the bias of 100 mV, a detection limit for the Hg2+ as low as 10 nM is achieved. Successful detection with minute quantity of the sample indicates that the sensor has great potential in practical screening for a wide population. In addition, the dimension of the active area of the sensor is 20 x 50 mu m(2) and that of the entire sensor chip is 1 x 2 mm(2), which make the Hg2+ biosensor portable. (C) 2015 Elsevier B.V. All rights reserved.