A membership function circuit which fuzzifies a nonfuzzy input signal to a fuzzy grade is needed for fuzzy information processing hardware systems. This paper describes the algebraic method for designing programmable membership function (PMF) circuits in current mode. In this method, the elementary functions r 1(ƒ, x) , r 2(ƒ,x) , and δ( x) are proposed. These functions are suitable for implementing a current mode circuit. The test chip of PMF designed by this method is fabricated in p-MOS integrated circuit technology. The characteristics of PMF are verified by this test chip and the spice ii simulation. The PMF has the following features: 1. (1) various shapes of membership functions can be produced by assigning six parameters; 2. (2) it exhibits low sensitivity to supply voltage (1%F.S./V for 8–14 V) and to temperature (0.07%F.S./°C for −55 to 60°C); 3. (3) it is suitable for real-time processing systems. (The speed of response is as high as 30 ns.) The PMF described here is indispensable for fuzzy information processing hardware systems.