Heat/mass transfer characteristics on the winglet top surface for the cavity squealer tip equipped with a full coverage winglet has been investigated experimentally with the variation of h/s (tip gap height-to span ratio) by employing the naphthalene sublimation technique. For a squealer rim height-to-span ratio of h(st)/s = 3.75% and a winglet width-to-pitch ratio of w/p = 10.55%, the tip gap is changed to be h/s = 0.34%, 0.68%, 1.02%, 1.36%, and 1.70%. On the winglet top surface, high local heat/mass transfer rate is found (i) at the sites of the leading edge tip gap vortices, (ii) in the flow separation/reattachment area on the pressure-side winglet, (iii) in the upstream outflow area on the suction-side winglet, (iv) in the downstream outflow area on the suction-side winglet, and (v) in the area where the cavity fluid is discharged toward the trailing edge. On the other hand, very low local heat/mass transfer rate is observed in two separate areas on the suction-side winglet upstream of the mid-chord. In the case of very low h/s, the two separate low heat/mass transfer areas cannot be identified. Instead, a new high heat/mass transfer area is found near the mid-chord on the suction-side winglet. Average heat/mass transfer rate on the winglet top surface tends to increase consistently with increasing h/s, but it is always lower than that on the tip surface of the plane tip with no winglet. (C) 2016 Elsevier Ltd. All rights reserved.