In a tree-structured ZigBee wireless sensor network, nodes close to the root of the tree (i.e.; hot-spot nodes) may exhaust their power earlier than those distant from the root due to heavy loads on packet forwarding. This hot-spot problem is inherent in tree-structured networks and may demand extra energy to recover from failures of hot-spot nodes. In this paper, the backbone-aware topology formation (BATF) scheme is proposed to alleviate the hot-spot problem. BATF utilizes power-rich nodes to form a backbone tree that does not suffer from the hot-spot problem. Each power-rich node independently initiates a ZigBee tree network that attracts associations from ZigBee-compliant devices in order to distribute packet-forwarding loads over a larger set of nodes. Issues of BATF such as the partition of address space and ZigBee-compliant routing are discussed in detail. Simulation results confirm that BATF does alleviate the hot-spot problem as it improves network lifetime as well as data collection capability. Comparisons with native ZigBee protocols show that the improvement comes from our protocol design rather than simply introducing power-rich nodes.