A substrate bias generator in which a junction point of the capacitance and the diode of a charge pump is connected to the ground point of the circuit (and of the further circuit on the substrate for which the bias is generated) via two or more series-connected transistors. During the charging period of the capacitance the transistors are (fully) conductive, hence the capacitance is optimally charged as the conductive transistors cause no (or hardly any) voltage drop. During the pumping cycle all transistors are diode-connected, to bring about a negative voltage with respect to the ground point at the junction point. This negative voltage is limited to the sum of the threshold voltages of the diode-connected transistors.