[en] During the RF test campaign-4, the prototype antenna for the KSTAR ICRF heating system was tested to verify its available maximum RF voltage and long pulse capability. As a result, the maximum standoff voltage was 40.4 kVp for a pulse length of 5 sec. It was limited by a breakdown on the teflon insulator used in transmission line. When the line voltage was 30.0 kVp, a RF breakdown occurred at t=66 sec, which was caused by the pressure increase in RFTC. A long pulse test showed the maximum standoff voltage was 15.1 kVp for a pulse length of 300 sec. It was limited by overheating of the antenna. The temperature profile on the front face of the prototype ICRF antenna was measured using an IR camera during a long pulse operation. For a test pulse of 30.0 kVp/66 sec, the maximum temperature was 374 .deg C, and it was 287 .deg. C for 15.1 kVp/300 sec. A 2-D magnetostatic calculation was performed to evaluate the heat load profile on the current strap and the Faraday shield. The measured temperature profile well agreed with the calculated heat load profile