biannually means occuring twice a year

bimonthly means occuring twice a month (or once every two months)

biweekly means occuring once every two weeks

semiannually means occuring twice a year

semimonthly means occurring twice a month

semiweekly means occurring twice a week

or just avoid these and use twice a year, twice a month, etc.

for a litle more confusion, biennially means occuring once every two years