When I studied literature in U, my professor said that "Gothic" describes a mood that is primarily gloomy and suggestive of the supernatural elements. It is a staple of the Romantic movement of the late 18th-early 19th century. "Gothic" shows the struggle between man and nature, while nature mirrors the turmoil inside the characters. The characters are often "haunted" by their own imagination and dark, repressed sides, while they are also disturbed by supernatural elements.
I don't know enough to agree or disagree with the professor.
Most SWs I've seen have dark elements but they're not exactly a deep exploration of the human psyche. Their mood can be full of dread and melancholy such as The Great Silence, but still I hardly recall a SW that had obvious supernatural elements.