A surface treatment method for a semiconductor substrate of the present invention is a treatment method of treating a main surface of a semiconductor substrate that has, on the main surface of the substrate, a pattern formation region in which a pattern having a concave-convex structure with a pattern dimension of 30 nm or less is formed and a pattern non-formation region in which no pattern is formed, the method including a surface treatment step of bringing a surface treatment agent composition including a silylating agent into contact with the pattern formation region and the pattern non-formation region on the main surface of the semiconductor substrate, in which, with respect to a surface of the pattern non-formation region after the surface treatment step, an IPA contact angle with 2-propanol is 2° or more at a room temperature of 25° C. and/or a water contact angle with pure water is 50° or more at the room temperature of 25° C.