N3
だけでなく(て)～も
Not only ~ but ~ also, Not just ~ but ~ also
アメリカだけではなく、韓国とチリにも行ったことがあります。
Not only the US, I have also been to Korea and Chile.
Explanation
「だけでなく～も」 means 'not only... but also...'. The fact is not limited to what was named first, and something else is true too, usually marked by 「も」 in the second half. It follows nouns, adjectives or the plain form of verbs: 「彼は英語だけでなく、中国語も話せる」 (He speaks not only English but also Chinese). It is the most common and natural 'adding' pattern in modern Japanese, fine in conversation, business e-mail and all kinds of writing.
Mixed up with
「だけでなく」 is very common in speech and writing with no special feeling. 「ばかりでなく」 is more written, often with emotion or surprise. 「のみならず」 (N2/N1) is a very stiff written form for official and political writing.
In speech it becomes 「だけじゃなくて / だけじゃなく」.