South Korea’s growth remained robust in early June thanks to a continued boom in the semiconductor sector. Exports adjusted for working-day differences rose 49.7% from a year earlier in the first 20 days of this month, according to customs office data released Monday. That compares with a 52.6% increase in the same 20-day period of May. On an unadjusted basis, shipments increased 60.4%, while imports rose 23.2%, leading to a trade surplus of $17.5 billion.