Printing element substrate, printhead, and printing apparatus

The present invention discloses a printing element substrate, a printhead, and a printing apparatus. The printing element substrate comprises a printing element, a MOS transistor having a drain terminal, a source terminal and a back gate terminal, the drain terminal being connected to a first power supply node for receiving a first voltage, and a source terminal and a back gate terminal being connected to the printing element, and a unit including a second power supply node different from the first power supply node, and configured to supply a second voltage to a gate terminal of the MOS transistor, wherein, when the first voltage is not supplied to the first power supply node, the unit controls a potential of at least one of the gate terminal and the drain terminal so that a potential difference between the gate terminal and the drain terminal becomes lower than the second voltage.