In this paper we present a bulk micromachined check valve with very high frequency and extremely low leak rates. The valve is designed to have a hexagonal orifice, a hexagonal membrane flap and three flexible tethers. The three elbow-shaped flexible tethers are used to secure the membrane flap to the valve seat and to obtain large flap displacement in the forward flow direction. A silicon-on-insulator wafer and deep reactive ion etching technology are used to implement this microvalve. A very simple fabrication process has been developed, and only two photolithographic masks are required. Preliminary fluidics testing on a 1.44 mm size check valve was performed. A maximum flow rate (deionized water) of 35.6 ml min−1 was obtained at a forward pressure of 65.5 kPa, and only negligible leakage rate was observed at a reverse pressure of up to 600 kPa. The frequency response of the valve in air was also measured and its first resonance frequency was found at 17.7 kHz.