A MID-SIZED sized Korean semiconductor firm named DI makes products with distinctly un-sexy names like “Monitoring Burn-in Tester” and “Wafer Test Board”. It has lost money in each of the past four quarters. And there have been no changes to its fundamentals that might explain why its share price should shoot up from 2,000 to 5,700 won (from $1.80 to $5.12) in the space of just three weeks—including another 15% gain today. But DI’s chairman and main shareholder, Park Won-ho is no ordinary mortal. He is the father of Park Jae-sang, better known as PSY (as in “psycho”). “Gangnam Style”, if you haven’t heard, is now number one in Britain’s pop charts and number two in America. Local retail investors—referred with the derogatory gaemi-deul (“ants”) by professionals—are piling into DI shares because of it. Quite how they expect the horse-dancing YouTube phenomenon of 2012 to help DI sell more of its Wafer Test Boards is a mystery. But convoluted investor logic is of course not a new thing. DI is merely the latest example of Korea’s “theme stock”—the local equivalent of the 17th-century Dutch tulip, Pets.com and the like going into 1999, or the Chinese walnut. One of the most common themes has been the marriage stock. When the son or daughter of a company owner weds a chaebol family member, an unusually generous wedding gift may arrive. Back in 2009, shares in a firm named Bolak ran up from 2,000 won to 9,000 won after the owner’s daughter married into the family behind LG. The effects were short-lived: Bolak shares now fetch a more earthly 3,110 won.

The upcoming presidential election has created another subcategory of theme stocks. Following Ahn Chul-soo’s emergence as a political force about a year ago, shares in his company, Ahnlab, ran up from about 20,000 won each to a peak of 167,200 won. Since he declared himself as a candidate, Ahnlab has been crashing: now each share fetches 82,000 won. Ahnlab’s price-earnings ratio is still 87, mind you.

There are worse cases. Excitable ants bid up shares in Daehyun, a clothing firm, by 350% last summer, due to an apparent link with another presidential contender, Moon Jae-in. A widely-circulated photograph of a man who looked like Daehyun’s CEO seated smiling with Mr Moon was all they needed.

The man in the photo of course was in fact not even the CEO in question. The Financial Services Commission (FSC believes that the photograph and accompanying fib was deliberately spread by an individual pump-and-dump artist who ended up making 1.1 billion won (around $1m) from the jump in Daehyun’s shares.

The presidential race is just getting into full swing. Despite the FSC’s warnings, it is likely that political theme-stock mania will reach new heights in the coming weeks. This correspondent interviewed Moon Jae-in back in August and, unlike Daehyun’s CEO, actually had his picture taken with him. Should you read of an English journalist in South Korea quitting his day job and striking it rich between now and the election, you’ll know what happened.