semiannually; every six months
Adverbial expression meaning something occurs once every half year.
This magazine is published semiannually.
I get a health checkup every six months.
毎月 means 'every month', a shorter interval than 半年ごとに.
Standard kanji-kana mixed spelling.
Kanji spelling using 毎; less common but still seen.
Compound of 半年 (half year) + ごとに (each, every).