Please see the translation below:
Xià xuéqī wǒ yào huí Zhōngguó le, yīncǐ bù néng zài gěi nǐmen shàngkè le.
下学期我要回中国了，因此不能再给你们上课了。
I will go back to China next semester, so I can’t teach you any more.
Learn the Chinese phrase “要yào” and “因此 yīncǐ” in this sentence. 
Chinese phrase “要 yào” in this sentence is used to indicate a future tense.
For examples:
国庆节我要去西安旅游。
The Chinese phrase “因此yīncǐ” is often used to begin a sentence about a result. It is often used with “由于 (yóuyú) because/ for the sake of” to form the sentence pattern “由于… 因此…” and “由于” can be omitted. For example:
Yóuyú wǒ yào jiābān, yīncǐ bù néng hé nǐ yìqǐ qù KTV le.
(由于)我要加班，因此不能和你一起去KTV了。
I have to work overtime, so I can’t go to the KTV with you.