Structure of days of the week

星期 (xīngqī) means "week" in Chinese. This is also used to indicate which weekday you are talking about.

Structure

Days of the week in Chinese are formed by the word "week" followed by a number:

Days of the week
Monday	Tuesday	Wednesday	Thursday	Friday	Saturday	Sunday
星期一	星期二	星期三	星期四	星期五	星期六	星期天
xīngqīyī	xīngqī'èr	xīngqīsān	xīngqīsì	xīngqīwǔ	xīngqīliù	xīngqītiān

Notice that Sunday is the only exception. Rather than a number, 天 (tiān) is used. More formally, Sunday is also referred to as 星期日 (xīngqīrì).

今天是 星期一 吗？Jīntiān shì xīngqīyī ma?Is today Monday?
明天 星期五，太高兴了。Míngtiān xīngqīwǔ , tài gāoxìngle.Tomorrow is Friday, I'm so happy.
星期一 我们要上班。Xīngqī yī wǒmen yào shàngbān.We will go to work on Monday.
星期二 我很忙。Xīngqī'èr wǒ hěn máng.I am busy on Tuesday.
你 星期三 要做什么？Nǐ xīngqīsān yào zuò shénme?What are you doing on Wednesday?
我们 星期六 和 星期天 不在上海。Wǒmen xīngqīliù hé xīngqītiān bùzài Shànghǎi.Saturday and Sunday we will not be in Shanghai.
上个 星期三 我跟他见面了。Shàng gè xīngqīsān wǒ gēn tā jiànmiànle.I met him last Wednesday.
这个 星期三 我有空。Zhè gè xīngqīsān wǒ yǒu kòng.This Wednesday I (have time) am free.
下个 星期四 是我的生日。Xià gè xīngqīsì shì wǒ de shēngrì.My birthday is on next Thursday.
我们每个 星期五 都去酒吧。Wǒmen měi gè xīngqīwǔ dōu qù jiǔbā.We go to a bar every Friday.