SEOUL—Some of South Korea’s biggest companies, along with law firms and a cottage industry of business consultants, are eyeing potential opportunities in North Korea, one of the world’s most difficult business environments.

After months of rapprochement—including summit meetings between North Korean leader Kim Jong Un and South Korean President Moon Jae-in, and one between Mr. Kim and President Donald Trump—hopes are rising for more open access to North Korea, a country of 25 million people with vast mineral reserves and lots of cheap labor.

Samsung C&T Corp . , the de facto holding company of South Korea’s biggest and best-known conglomerate, created a North Korea task force in May, staffed by an executive and three managers.

Samsung’s construction arm, which has built some of the world’s tallest skyscrapers and is building subway lines in Singapore and Riyadh, Saudi Arabia, sees opportunity in the North as economic growth slows in the South.

The Samsung task force is following global developments related to North Korea, attending forums and seminars on economic cooperation between the Koreas and looking at potential areas for opportunities, a spokesman said.