Several problems are required to be solved to apply the geographical routing protocol Greedy Perimeter Stateless Routing (GPSR) in wireless sensor networks. First, GPSR is designed with the assumption of links with bidirectional capability (symmetric links). This has to be modified in order to effectively use the energy available with the nodes. Second, due to dynamic nature of the sensor networks, data consistency can not be maintained when home nodes change. In this paper modified GPSR algorithm is proposed to attempt to solve these problems. The modification proposed is to make use of a Hierarchical Energy Tree (HET) constructed using the available energy in each node. Using this HET the paper suggests either a bidirectional link or unidirectional link with each node. The GPSR algorithm also makes use of a routing metric based on the energy in each node. Thus an Energy Aware GPSR algorithm using the HET (HETEA-GPSR) is proposed. The algorithm is implemented in ns2. Simulations are carried out to evaluate the performance of the proposed algorithm. The results show that the GPSR-EA performs well in terms of packet delivery, throughput and average energy consumption.