This paper proposes a virtual touchpad human computer interaction (HCI) based on the fingertip hand gesture recognition (FHGR) method for smartphone with depth camera. The virtual touchpad HCI requires less computing power and memory resource than the conventional hand gesture recognition (HGR) methods. It consists of three modules: (1) open hand identification, (2) active fingertip detection and tracking, and (3) fingertip hand gesture recognition (FHGR). First, the handshape region is segmented and divided into three component regions: arm, palm, and fingers. Second, we locate the fingertips and then detect the active fingertips. Finally, the trajectory of every active fingertip is analyzed for FHGR. The two major contributions of this paper are (1) development of a real-time FHGR method with high recognition accuracy and (2) implementation of a virtual touchpad HCI for the smart phones.