South Korea's exports likely posted their biggest drop in nearly three years in March, dragged down by sluggish demand for things like semiconductors, a Reuters survey showed on Thursday. South Korean exports are expected to have fallen 17.5% in March from a year earlier, compared with a 7.5% drop in February, according to the median forecast of 18 economists in the survey. That would be the biggest drop since May 2020 and the sixth straight month of year-on-year declines in exports.