We develop a method for direct measurement of thermal conductivity of nanowires, consisting of a microelectrothermal test device and a complementary parameter estimation algorithm. Simulations of a simplified version of the problem show how differential measurements can address the problem of parasitic heat loss, and examine several different parameter estimation schemes. As reported elsewhere, measurements have been performed on aluminum nanowire arrays, with excellent results. Several design modifications are required to accommodate semiconducting samples. A device design for silicon nanowire arrays is presented. A simulation study suggests that these devices will also perform extremely well.