An 84‐GHz electron cyclotron heating (ECH) system is being installed on the KSTAR tokamak. KSTAR adopts ECH‐assisted start‐up for the flexibility and reliability of the KSTAR operation with the plasma breakdown voltage reduced. The available maximum power of the 84 GHz ECH system is presently 500 kW with maximum duration of 2 s. Currently, the second harmonic ECH‐assisted start‐up is under consideration because a low toroidal field of BT∼1.5 T is desirable for safety and also for the high‐beta experiments in the initial operation phase. The studies in this paper are on the effectiveness of the second harmonic breakdown using a 0‐D time dependent plasma evolution code and the comparison with the recent DIII‐D experimental results on the second harmonic pre‐ionization