How to express 'semi-' and 'mid-' is a question I've had to answer quite a few times. That's why I decided to address it today.
The main way used in English is through prefixes.
The first such prefix is 'mid'
midday- noon, midday, afternoon
midnight- midnight, nocturnal
midway- (along) the middle of the way
midsummer- the middle of summer
mid June- mid-June
middle-aged- middle-aged
middle-sized- of medium height
middle-weight- boxer in a middle category
A similar prefix is 'semi'
semi-educated- semi-educated
semi-opaque- semi-transparent
semi-circle- semicircle
semi-official- semi-official
semiconductor- semiconductor
semi-manufactured /goods/- semi-finished goods
'hemi' is also used,
hemisphere- hemisphere
hemicycle- semicircle
as well as 'half'
half-brother- half-brother
half-circle- semicircle
half-price- half price
Very rarely 'demi'
demigod- demigod