A glitch detector includes a sensing circuit, a glitch-to-pulse generator and a comparing circuit. The sensing circuit generates a glitch voltage and at least one reference voltage based on a first power supply voltage. The glitch-to-pulse generator receives the first power supply voltage or the glitch voltage, and generates at least one pulse voltage including a pulse when the glitch occurs on the first power supply voltage. The comparing circuit generates at least one detection voltage by comparing the glitch voltage with the at least one reference voltage based on the pulse included in the at least one pulse voltage. The at least one detection voltage is activated when the glitch occurs on the first power supply voltage.