Recently proposed key-value SSD (KVSSD) provides the popular and versatile key-value interface at the device level, promising high performance and simplified storage management with the minimal involvement of the host software. However, its I/O command set over NVMe is defined on a per key-value pair basis, enforcing the host to post key-value operations to KVSSD independently. This not only incurs high interfacing overhead for small key-value operations but also makes it subtle to support transactions in KVSSDs without a software support. In this paper, we propose compound commands for KVSSDs. The compound command allows the host to specify multiple key-value pairs in a single NVMe operation, thereby effectively amortizing I/O interfacing overhead. In addition, it provides an effective way for defining a transaction comprised of multiple key-value pairs. Our evaluation using a prototype KVSSD and an in-house KVSSD emulator shows promising benefits of the compound command, with improving the performance by up to 55%.