お腹が空く

Etymology
Phrase composed of.

Verb

 * 1) to become hungry

Usage notes
Most often encountered in the perfective form, as (onaka ga suita, literally “[my] belly has become empty”, used idiomatically to mean “[I] am hungry”).

Often found in reference materials with onaka spelled as or  instead; see those entries for details. The spelling is used more often for this  sense.