A level shifter transfers a first voltage signal to a second voltage signal. The level shifter comprises a comparison circuit, a delay circuit, and a selection circuit. The comparison circuit generates a first signal according to the comparison result between the first voltage signal and the reverse-phase signal of the first voltage signal. The delay circuit generates a second signal according to the first voltage signal. The selection circuit receives the first and the second signals and chooses the higher voltage one from the first signal and the second signal to be the second voltage signal.