A pixel sensor that provides image sensing under radiation or space environment is disclosed. The pixel sensor includes a readout circuit and a first reset circuit. The readout circuit converts optical image signals to electronic signals, and includes p-type transistors and an n-type photosensitive element. The first reset circuit is configured to provide a reset level for a pixel output, and also includes p-type transistors. The use of p-type transistors and n-type photosensitive element provides radiation hardness without any radiation protective enclosure.