A solid-state neutron detector for detecting both fast and slow neutrons comprises two layers, one of which contains a neutron-sensitive first material and the other of which contains a semiconducting second material containing hydrogen, the first and second materials meeting to form a rectifying junction therebetween. The neutrons are detected by detecting electron-hole pairs migrating in opposite directions relative to the junction. The electron-hole pairs are created by energetic free protons produced by the fast neutrons travelling through the second material and by energetic reaction particles produced by the slow neutrons travelling through the first material. Stacking several of these detectors next to each other enhances overall sensitivity for detecting both fast and slow neutrons.