Abstract We studied the thermal response of superconducting MgB 2 detectors by irradiating 20-ps pulsed laser. We produced a 1-μm or 3-μm line and space meandered line of MgB 2 film on a sapphire substrate. We used a low-noise HEMT preamplifier at 23 K or a low-noise preamplifier at room temperature to recover tiny signals. Systematic studies of the transient signals with various bias currents and temperatures are reported to optimize measurement conditions. The maximum operating speed of our MgB 2 detector was found to be 1.3 ns when the fast electronics was used. Our MgB 2 detector can be used as a neutron detector by using nuclear reaction between neutron and 10B in MgB 2.