The kanji is . Let me describe how you can check.
When you type the expression in with your IME, often a dictionary with appear with usage information. On my system, when I type , to the side a window with details on , , , and appears. For it says: ⇒
Note arrow suggesting that it be written in hiragana. Also note the * which indicates that it is not included in basic kanji, and hence is not typically written in kanji.
Also, the dictionary is often useful. Quote:
> ×
>
> ② ――
Note the × before the headword. This indicates that it is not generally written in kanji. Same details as above.