After reviewing Wikipedia article 語種, which states that a word is either 和語【わご】, 漢語【かんご】, 外来語, or 混種語【こんしゅご】, I can safely answer that
電子レンジ belongs to 混種語 group.
A 混種語 (mixed type word) is a combination of two or more words (hence, is also a 複合語【ふくごうご】) of differing categories 和語, 漢語, 外来語.
- 和語: native Japanese, which include most 動詞 and 形容詞. Includes 固有語【こゆうご】.
- 漢語: borrowed from ancient China
- 外来語: borrowed from other than above. Includes 和製外来語, which includes 和製英語.
There are two component words in
レンジ: 外来語 which is corrupted to 和製英語 by usage, see my old answer below for my postulation.
Methinks it's classified as compound word (複合語). The words in a compound can be of any origin, and of any class (verb, noun), so it's difficult to say if a compound like 電子レンジ is 和製英語 or not. Maybe you can classify as:
- "purely 外来語": ガスレンジ,
- "purely 固有語": 夜明け, 旅立つ
- can't think of pure compound 和製英語, because words like ボールペン in my opinion is considered as one word in Japanese. I don't know if ノートパソコン qualifies, as パソコン is a contraction rather than a 和製英語.
- "mixed": 電子レンジ, ビニール袋
Interesting to note here is that although words like レンジ and ビニール are originally 外来語, their usage in such compounds may "corrupt" them into 和製英語 (e.g. レンジ in 電子レンジ is actually oven, and ビニール in ビニール袋 is just plastic). In that case, classifying ガスレンジ as "purely 外来語" might be controversial.