The first half of 2015 is winding to a close, and so far, it has not been pretty for Intel (INTC 1.74%). The shares are down nearly 15% year-to-date, solidly underperforming the PHLX Semiconductor Sector Index ETF and the broader S&P 500, both up about 1.5% over the same period.

This poor showing has been driven largely by a weaker PC market than what Intel and investors were expecting at the beginning of 2015. Intel had previously guided to roughly flat PC chip shipments and slight selling price declines, but it is now calling for a mid single-digit unit decline.

Following a negative data point from memory maker Micron, which said PC builds had declined "well below seasonally slow demand in the first half of the year," Intel stock lost another 3% last Friday.

As an Intel investor, I would like to look at three potential catalysts that shareholders should keep an eye on during the second half of the year.

PC build activity
PC processors represent the majority of Intel's microprocessor units and revenue, so its financial performance is highly dependent on PC sales. Weak sales during the first half of 2015 have been exacerbated by the fact that PC vendors have been burning inventory rather than building it.

This inventory reduction, according to Intel CFO Stacy Smith, took place during the first quarter of 2015 and continued through the second quarter of the year. Then, according to Smith, Intel expects PC vendors to rebuild their inventory to more "normal" levels.

When Intel releases its second quarter earnings results, it will be critical to see whether management stands behind the belief that the inventory rebuilding trend will play out. This will be evident from the guidance Intel issues for the third quarter.

Data center growth levels
During the investor meeting back in late 2014, Intel forecasted that its data center group would grow sales by over 15% during 2015 and for operating profit to "grow faster than revenue." In the first quarter, this business grew by slightly over 19%, which was quite impressive.

If Intel is able to grow its data center group revenue by significantly more than 15% (along the lines of say, 17 to 18% for the full year), then this could be viewed quite positively by investors, creating a "buffer" for any PC weakness.

Guidance for 2016
In November, Intel is expected to host its annual investor meeting. At this event, the CEO will give his "big picture" overview of the company trajectory, the various general managers will then speak about their respective business units, and the CFO will discuss financial guidance for fiscal 2016, usually by business segment.

A key point will be the financial guidance the company issues for 2016. According to data from S&P Capital IQ, full-year 2016 revenue is forecasted at $58.1 billion with earnings per share of $2.40.

If Intel guides to even stronger numbers, then that should serve as a bullish signal for investors to buy in. However, lower guidance will likely have a pronounced reverse effect as skittish investors, already reeling from recent losses, look elsewhere for opportunities.