Analogous to the electronic diode, a thermal diode transports heat mainly in one preferential direction rather than in the opposite direction. Phase change thermal diodes usually rectify heat transport much more effectively than solid state thermal diodes due to the latent heat phase change effect. However, they are limited by either the gravitational orientation or one dimensional configuration. On the other hand, solid state thermal diodes come in many shapes and sizes, durable, relatively easy to construct, and are simple to operate, but their diodicity (rectification coefficient) is always in the order of eta similar to 1 or lower. Thus, it is difficult to find any potential applications. In order to be practically useful for most engineering systems, a thermal diode should exhibit a diodicity in the order of eta similar to 10 or greater. In this study, a passive solid state thermal diode with shape memory alloy is built and investigated experimentally. The diodicity is recorded at about 90. This promising result could have important applications in the development of future thermal circuits or for thermal management. (C) 2015 Elsevier Ltd. All rights reserved.