Event-triggered control aims at reducing the resource utilization, especially the communication over the feedback link, while guaranteeing a certain control performance. Although setpoint tracking problems are common in practice, the majority of the proposed approaches in literature focus on regulation problems. Therefore, an event-triggered PI control design strategy with guaranteed performance is proposed in this paper, where both the event-triggering condition and the PI controller are implemented periodically. Based on a quadratic cost function, the PI control design problem is introduced and formulated as an LMI optimization problem. Comparisons with other approaches in the literature are made by simulation and by experimental studies to demonstrate the effectiveness of the proposed strategy.