〜ばかりでなく

not only

"Not only X, but also Y": adds a second, often greater, point.

Readings

How to form it

Put ばかりでなく after a noun or a plain form, and use も in the second half: 日本(にほん)ばかりでなく、海外(かいがい)でも有名(ゆうめい)だ.
な-adjectives take な: 便利(べんり)なばかりでなく.
It sounds formal. だけでなく means the same and is more common; ばかりか is more emphatic.
だけでなく has the same additive meaning in a more neutral register. In casual speech, だけじゃなく is common; the second point can be marked with も or stated as a parallel predicate.

彼(かれ)は頭(あたま)がいいばかりでなく、優(やさ)しい。

He's not only clever but kind as well.

日本(にほん)ばかりでなく、海外(かいがい)でも有名(ゆうめい)だ。

She's famous not only in Japan but abroad too.

この店(みせ)は安(やす)いだけでなく、便利(べんり)です。

This shop is not only inexpensive but also convenient.

この部屋(へや)は広(ひろ)いだけじゃなく、明(あか)るいです。

This room is not only spacious but also bright.