We claim the ornamental design for a semi-truck, as shown and described.
FIG. 1 is a front and right perspective view for a semi-truck showing our new design;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a right side view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a front view thereof; and,
FIG. 7 is a rear view thereof.
The broken lines in the drawing views represent unclaimed portions of a semi-truck, which are included for the purpose of illustrating unclaimed environment only, and forms no part of the claimed design.