what is the meaning of semi-fixed cost?

Semi-fixed cost also known as semi-variable cost.

Semi-fixed cost is formed by both fixed and variable costs. Semi-fixed cost 由固定及非固定成本組成。

Costs are fixed for a set level of production or consumption, becoming variable after the level is exceeded.成本在生產時是固定的，但超過某程度時，成本變成非固定。

Labor costs in a factory are semi-variable. The fixed portion is the wage paid to workers for their regular hours. The variable portion is the overtime pay they receive when they exceed their regular hours. 工人的每月薪金是固定的，但ot就是variable cost.

電費不是semi-variable cost，因電費是按用量付款的。

但電話費有時候是semi-variable costs。

客人與電訊商的合約裡，手機的每月電話費是固定的，額外的分鐘便是variable costs.
例如：$50/500分鐘是合約所訂的服務計畫，第501或以上的分鐘的電話費便是variable costs。

可是，家居固網電話大部份情況是fixed cost ，因為費用不會因用量的多少而改變。
除了是打IDD的時候，這點需要留意。