A couple of years back, I wrote about the great prospects I saw for the Filtronic (LSE: FTC) share price. Back then, this share was nowhere close to making it into the FTSE 250, let alone the FTSE 100.

Back in August 2024, the share had already tripled since the start of that year. Since I wrote about it then, the Filtronic share price has soared 437%.

That means that, over the past five years, it is up a staggering 4,622%.

Could this just be the beginning?

Knocking at the FTSE 250 door, for now

The rise means the company now commands a market capitalisation of £935m. That is comfortably larger than many existing FTSE 250 members.

If it can sustain its current market cap, I think there is a strong chance we could see Filtronic joining that index in coming months. Index membership is due to be reviewed next month.

But I have my eyes on a bigger goal: the blue-chip FTSE 100 index.

Its smallest member by market capitalisation at the moment is Berkeley Group, with a market cap of £3.1bn. That is over triple Filtronic’s current market cap.

Still, with Filtronic’s meteoric rise in recent years, that sort of growth could be achievable.

Right place at the right time

Can that growth last?

After all, Filtronic is widely seen as a growth story but at the interim point this year, reported revenues actually showed a slight decline, from £25.6m in the prior year period to £25.3m this time around. Profit fell even more sharply, from £6.7m last time to £2.6m.

Those numbers might not seem impressive. Arguably, though, they reflect a business moving from one stage of its development to another.

Filtronic’s business with SpaceX has been very large already. But it could get much bigger from here. Indeed, in its interim results, Filtronic reported its largest ever contract with the space company, valued at $63m.

It has also been working hard to diversify its customer base as currently there is a concentration risk given how important SpaceX is to it.

Last month, Filtronic announced an order from an existing European defence customer for a new wide-bandwidth solution. The order size was modest but could lead to bigger things in future. That followed the prior month’s announcement of an $8m contract with a US firm for Filtronic’s Amplifier technology.

The manufacturer’s proprietary know-how is in demand just as space and defence demand is surging. That could see revenues and profits soar over time. It entered the second half of its current financial year with a record order book.

I’m watching not buying

I sold my Filtronic stake a while back for what I thought was a reasonable profit, though the share has since moved far higher.

Currently it sells for 101 times earnings. I see that as too pricey (and note, there have been multiple director share sales lately).

I think the company’s sales prospects are great and it has strong pricing power that could help it grow earnings. If it does that, I believe we could yet see it in the FTSE 100.

But the current share price looks too high to me. I will not be investing, but instead will hunt for other more attractively priced growth shares.

Should you invest £5,000 in Filtronic Plc right now?

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Christopher Ruane holds no position in any of the companies mentioned.