In chess, a half-open file (or semi-open file) is a file with pawns of only one color. The half-open file can provide a line of attack for a player's rook or queen. A half-open file is generally exploited by the player with no pawns on it.

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

Both the c- and d-files are half-open, with each player's rook in position to capitalize.

Many openings, such as the Sicilian Defense, aim to complicate the position. In the main line Sicilian, 1.e4 c5 2.Nf3 d6 (or 2...e6, or 2...Nc6) 3.d4 cxd4 4.Nxd4, White obtains a half-open d-file, but Black can pressure White along the half-open c-file.

In positions where White has no pawns on a file but Black has one pawn or more on that file, the position is considered to be half-opened for White. In cases where Black has no pawns on a file but White has one or more pawns on that file, the position is considered to be half-opened for Black.

A pawn break occurs when a pawn captures or advances in a way that opens or half-opens one or more files. The demolition of the pawn structure is a common theme in positions with half-open files, since doubled pawns or isolated pawns may create half-open files.