In this work, we report on ElecFET (Electrochemical Field Effect Transistor) devices potentially of interest for the detection of different molecules in solution. ElecFET are electrochemical microsensors in liquid phase, based on two elements: (i) a pH-sensitive chemical field effect transistor (pH-ChemFET) and (ii) a metallic microelectrode deposited around the sensitive gate. The coexistence of these two elements combines (i) potentiometric and (ii) amperometric detection effects at the microscale. Design, fabrication and experimental validation of ElecFETs based on silicon and polymer micro-technologies, are reported. We first demonstrate the detection of hydrogen peroxide (H2O2) in solution, showing a sensitivity of 5 mV/mM in the [10-100mM] concentration range. The ElecFET concept is then extended to the detection of glucose and lactate in the [1 – 30 mM] and [1 – 6 mM] concentration range respectively. The sensitivities are between 2-6 mV/mM and 8-20 mV/mM respectively.