Provided are a system in package (SIP) semiconductor device suitable for efficient power management, and a method of managing power of the SIP semiconductor device. The SIP semiconductor device includes chips including first and second chips. Each of the chips includes an alive block, a local interface, and an intellectual property (IP) block. The alive block is continuously supplied with power in order to continuously be in an on-state. The local interface transmits/receives data to/from other chips. The IP block individually stores and processes data. The alive blocks of the chips are connected to each other through a first signal line unit for transmitting a signal required to wake up or initialize the chips. The alive blocks control power to the chips, respectively, in response to an external wake-up instruction signal or the signal transmitted through the first signal line unit. Therefore, power can be efficiently managed since power that is supplied to the chips of the SIP semiconductor device is managed by the alive blocks or the local interfaces of the chips.