A voltage level shifter for shifting an output signal from a first voltage level to a second voltage level and then to a further boosted second voltage level is disclosed. The voltage level shifter comprises: an input for receiving an input signal; an output for outputting an output signal; a first power supply input for connecting to a first voltage source supplying said first voltage level; a second power supply input for connecting to a second voltage source supplying said second voltage level; and a third power supply input for connecting to a third voltage source supplying said boosted second voltage level; said voltage level shifter being responsive to a predetermined change in said input signal to isolate said first power supply input from said output and to connect said second power supply input to said output and being responsive to said output signal attaining a predetermined value to connect said third power supply input to said output and to isolate said second power supply input from said output.