Highly ion-conducting properties in heterostructure composites and semiconductors have drawn significant attention in recent years for developing new electrolytes in low temperature solid oxide fuel cells (LT-SOFCs). In this work, a new semiconductor heterostructure composite SrFe0.2Ti0.8O3-delta, (SFT)-ZnO consisting of p-type SFT and n-type ZnO is proposed and evaluated as an electrolyte in LT-SOFCs. Electrochemical studies reveal that the prepared SFT-ZnO is a mixed ion-electron conductor possessing a high ionic conductivity of 0.21 S cm(-1) at 520 degrees C and the assembled SFT-ZnO fuel cell can achieve a favorable peak power output of 650 mW cm(-2) along with high open-circuit voltage (OCV) of 1.06 V at 520 degrees C. By referring the semiconductor conduction types and energy band parameters of SFT and ZnO, a p-n bulk-heterojunction effect is proposed to describe the electronic blocking and ionic promotion processes of SFT-ZnO electrolyte in a fuel cell. Our work suggests a new insight into the design of effective LT-SOFC electrolytes by using semiconductor heterostructure material. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.