上に【うえに】

上に means "on top of that", "not only… but also": a second point piles onto the first. It follows the plain form of a verb or い-adjective, a な-adjective with な, and a noun with の or である. The second half often has も.

Both points go the same way

Both halves are good news, or both are bad. To set a good point against a bad one, use けど or のに instead.

• × この料理はおいしい上に、高い → この料理はおいしいけど、高い

No request after 上に

The second half states a fact. An order, a request or an invitation does not follow 上に: ×安い上に、買ってください. To give reasons for a request, use し or から.

上に or し

し also lists points, but loosely and in conversation, and it often gives reasons. 上に stacks one point on another and sounds more written.

The same 上に after a noun with の is also the plain place word, "on top of": つくえ机のうえ上にほん本がある, "there's a book on the desk". The "in addition" 上に is followed by a second statement, usually with も.