KT Corp, South Korea's biggest fixed-line operator, announced last week its CEO, Lee Suk-chae, was resigning after prosecutors raided its headquarters amid a widening corruption probe.
Posco and KT Corp have often seen CEOs quit before their terms expire when a new government takes office because the companies were once state-owned and the government retains a large amount of influence over their operations.
"Despite challenging business conditions, Posco has reported strong performances, but I've decided to leave so that a new leadership can lead Posco's growth as a leading global company," Chung said in a statement.
He said that there has been no external pressure for him to leave. Posco plans to form a CEO nomination committee, which will recommend a candidate at its shareholders meeting scheduled in March.
Local media reports said Park's election campaign aide, Kim Jong-in, and SK Innovation CEO Koo Ja-young, who was a former managing director at Posco, are among the potential candidates to succeed Chung.